In earthmoving scrapers a number of the implement components on the scraper portion must be controlled from the tractor portion by the operator. As a result, numerous high pressure hydraulic hoses often must cross the articulated hitch between the tractor and scraper portions, or an alternate arrangement selected, involving locating the control valves on the scraper portion and operating them by remote control systems.
While such an alternate arrangement has many advantages, it does require a safe, reliable, positive acting remote control system to operate the control valves on the scraper portion, as the operator does not have any direct physical access to the main control valves. Because of these requirements, pilot-operated control systems using positive bleed arrangements have been used, such as disclosed in U.S. Pat. No. 3,515,032 which issued to J. E. Dezelan et al. on June 2, 1970. Also see U.S. Pat. No. 3,048,978 which issued to Hare on Aug. 14, 1962 and U.S. Pat. No. 3,160,174 issued to Schmiel on Dec. 8, 1964 and U.S. Pat. No. 3,220,318 issued to McGuire on Nov. 30, 1965. The current invention is related to a bleed control system similar to the one disclosed in some of these patents.
One of the principal objectives of this invention is to provide a pilot control system for scrapers that is suitable for operating open center control valves, so needless horsepower loss will not occur by pumping large volumes of hydraulic fluid at high pressures over relief valves.
Another object is the provision of a pilot-operated system which includes fail-safe features for earthmoving scrapers.